1. Field of the Invention
The present invention relates to a nanoparticle composition, and more particularly to a nanoparticle composition containing azolium and N-heterocyclic carbene compounds.
2. Description of the Related Art
Cancers are a large family of diseases that involve abnormal cell growth with the potential to invade or spread to other parts of the body. Cancer is a major public health problem in the world. In the United States, it is expected to become the leading cause of death in the next few years. On the other hand, the survival rate for those suffered from cancer increases in recent years. This could be attributed mainly to the advancement of new chemotherapeutic agents. Cisplatin is one of the chemotherapeutic agents that have been widely applied to treat cancers. However, because of its high toxicity and drug resistance, cisplatin is not an ideal anticancer drug. Therefore, there is a need to find new anticancer drugs having low toxicity and high therapeutic effects.
There is a surge of interest in the medicinal application of gold nanoparticles (AuNPs) because of their low toxicity,1 biocompatibility,2 and high drug accumulation.3 In order to disperse AuNPs in phosphate-buffered saline or other medium solutions for medical applications, capping agents are necessary.4 For this purpose, AuNPs capped with oligonucleotides, peptides, lipids, antibodies, ammonium salts, amines and citrate are used as drug carriers, imaging agents,5 or a photo-responsive therapeutic agents.6 
Imidazolium salts are a widely studied family of compounds, especially for their medical applications including, for example, treatment of microbial infections, cancers, fibrotic diseases and so on (US 2007/0043016, US 2014/0142307, WO 2009/096905). Imidazolium salts have been used to prepare metal NPs. Thus prepared NPs often have imidazolium salts as the capping or stabilizing agents. In few cases N-heterocyclic carbenes (NHCs) derived from imidazolium salts have also been found on the NP surface. NHCs are good σ-donor ligands, able to form strong bonds with metals of different oxidation states. The first proposition of possible NHC formation on Ir(0) nano cluster surface was evidenced by the observation of H-D exchange of imidazolium ring protons.7 Up to now, different approaches have been developed to prepare NHC-coated metal NPs.7-8 In one case, reduction of metal NHC complexes has been employed to produce metal NPs.8h As a different approach, displacement of capping agent on metal NPs by preformed NHC has been reported.8c, 8d, 8g Alternatively, azolium salts with metallate anions as precursors have been utilized to form NHC capped metal NPs via deprotonation and reduction processes.8e, 8f 